Mars meteorite sheds light on planet’s environmental history

Nasa’s Mars Rover Opportunity is investigating a metallic meteorite the size of a large watermelon, larger than any other known meteorite on Mars, that is providing researchers more details about the Red Planet’s environmental history.

Scientists calculate that the rock, dubbed “Block Island,” is too massive to have hit the ground without disintegrating unless Mars had a much thicker atmosphere than it has now when the rock fell.

It was discovered two weeks ago, when Opportunity had driven approximately 600 feet past the rock in a Mars region called Meridiani Planum.

An image the rover had taken a few days earlier and stored was then transmitted back to Earth.
The image showed the rock is approximately 2 feet in length, half that in height, and has a bluish tint that distinguishes it from other rocks in the area.

The rover team decided to have Opportunity backtrack for a closer look, eventually touching Block Island with its robotic arm.

“There’s no question that it is an iron-nickel meteorite,” said Ralf Gellert of the University of Guelph in Ontario, Canada.

“We already investigated several spots that showed elemental variations on the surface. This might tell us if and how the metal was altered since it landed on Mars,” he said.

The microscopic imager on the rover’s arm revealed a distinctive triangular pattern in Block Island’s surface texture, matching a pattern common in iron-nickel meteorites found on Earth.

“Normally this pattern is exposed when the meteorite is cut, polished and etched with acid,” said Tim McCoy, a rover team member from the Smithsonian Institution in Washington.

“Sometimes it shows up on the surface of meteorites that have been eroded by windblown sand in deserts, and that appears to be what we see with Block Island,” he added.

Opportunity found a smaller iron-nickel meteorite, called “Heat Shield Rock,” in late 2004.
At about a half-ton or more, Block Island is roughly 10 times as massive as Heat Shield Rock and several times too big to have landed intact without more braking than today’s Martian atmosphere could provide.

“Consideration of existing model results indicates a meteorite this size requires a thicker atmosphere,” said rover team member Matt Golombek of NASA’s Jet Propulsion Laboratory in Pasadena, California.

“Either Mars has hidden reserves of carbon-dioxide ice that can supply large amounts of carbon-dioxide gas into the atmosphere during warm periods of more recent climate cycles, or Block Island fell billions of years ago,” he added.